The field of the present invention is Rankine cycle vapor pressure or steam engines obtaining their driving heat energy from a chemical reaction other than the usual combustion of fuel with oxygen from the air. Particularly, the theoretical possibility of utilizing the reaction energy of a reactive metal fuel such as Aluminum, Magnesium, or Lithium, and alloys or hydrides of these and similar reactants, with an "oxidizer" such as hydrogen peroxide, Freons, sulfur hexaflouride, water, and others, has been recognized for many years. However, the technical difficulties and conflicts standing between a theoretical construction of such a power system and a practical apparatus which is functional outside of the laboratory are legion.
By way of example, many of the fuel-reactant combinations proposed in the past require that the fuel be raised above ordinary ambient temperatures in order to permit reaction with the reactant. Such a heating requirement necessitates that some heating means, such as electrical heating coils or pyrotechnic chemicals be provided. In the former case, a significant start-up delay is incurred while a portion or all of the fuel is raised to reaction temperature. In the latter case, the pyrotechnic chemicals, which are or may be considered to be low velocity explosives, present the possibility of rupturing the reaction chamber and escape of highly reactive or toxic fuels. Such pyrotechnic heating chemicals also frequently produce a quantity of gaseous reaction products which must be contained within the reaction chamber, or else vented therefrom while preventing loss of fuel.
Another undesirable aspect of many previously proposed fuel-reactant systems is that intermediate reaction products or end reaction products are formed which on the one hand inhibit further progress of the reaction between the fuel and reactant, or on the other hand freeze at a temperature higher than the desired reaction chamber temperature. In the one case, complex structures and methods have been proposed to cure the shortcoming by removing the intermediate or final reaction product from the reaction chamber. Alternatively, only a portion of the fuel could be brought into contact with the reactant so that reaction products could not contaminate the remaining fuel. Again, complexity is increased.
The problem of the reaction intermediates or final products freezing at too high a temperature presents the difficulty that the reaction chamber may soon become filled with a "slush" of frozen reaction products in a slurry of molten fuel. Similarly, the high-freezing constituents present in the reaction chamber may form a "frost" or crust on the coolest surfaces present. These cool surfaces will ordinarily be heat transfer surfaces where it is desired to transfer heat from the chemical reaction for utilization in a steam or vapor pressure Rankine cycle engine. Such a crust on the heat transfer surfaces will ordinarily have a relatively high insulation value in comparison with the molten fuel. As a result, the crusted reaction products themselves progressively inhibit heat transfer from the reaction chamber to the engine.
A novel approach to the above-discussed problem is presented by the copending patent application Ser. No. 681,160, now U.S. Pat. No. 4,643,166, issued Feb. 17, 1987, of Palmer Wood, having the same filing date and assignee as this application (hereinafter the Wood application). In the Wood application a fuel is reacted with water in the absence of oxygen to produce heat and hydrogen. The heat from this reaction is used to produce water steam. The hydrogen is burned with oxygen in a separate second reaction chamber to produce super heated steam. The steam from the first reaction chamber is used as a coolant and diluent in the second reaction chamber so that steam flowing from the second reaction chamber to a turbine, or other expander, has a metalurgically acceptable temperature. The disclosure of the Wood application is hereby incorporated herein by reference to the extent necessary for a complete understanding of the present invention.
A shortcoming of the invention of the Wood application discovered by the present inventors is that a hydrogen bearing reaction intermediate is formed which initially partially prevents the evolution of the hydrogen from the first reaction chamber. As the reaction progresses, the reaction intermediate further reacts to release the bound hydrogen. The result is that over the period of the reaction, the rate of hydrogen production is at first relatively low, reaches a stable plateau, and then raises above the plateau as the fuel supply is consumed.
A consequence of this nonuniform rate of hydrogen production is that the power output of the Rankine cycle steam engine is relatively low initially and cannot be increased until the hydrogen production rate of the chemical reaction chamber increases. Understandably, this sluggish initial power output of such a system is undesirable in almost every prospective application. Additionally, the nonuniform rate of hydrogen production creates many difficulties in controlling the power output level of the Rankine cycle engine.
Conventional reaction chambers, fuel-reactant combination's, and methods of operating engines of the above-defined character are presented in United States Patents: